The energy for operating a power supply grid is supplied by various and different types of power stations. Herein, most of the power stations, such as nuclear power stations, coal-fired power stations, gas-fired power stations, wind turbines, biogas plants, or solar power plants, are nothing but energy generators for feeding energy into the non-local power supply grid. For example, non-local power supply grids are distribution networks and transmission networks, such as they are operated in Germany by Amprion, 50 Hertz, Tennet, and TransnetEnBW. These transmission networks are a part of the wide area synchronous grid in Europe. In their capacity as mere energy generators, the power stations mentioned above cannot absorb any extra energy from the grid and store it in case of need. In contrast, energy storage systems can be used to collect energy from and release it to a power supply grid. For example, energy storage systems are central energy storage systems, such as pumped storage power stations, or decentralized energy storage systems, such as battery storage devices or flywheel energy storage units. Pumped storage power stations are energy storage systems that are largely not subject to changes in weather and, as a general rule, are therefore always available. Usually, central energy storage systems are designed for a large capacity. Due to the available capacity, such systems are adapted to provide reserve energy for the non-local power supply grid in order to take appropriate effect in the non-local power supply grid. Depending on their overall size, pumped storage power stations may have a capacity of several 100 MW and more wherein, however, the generators are, in most cases, designed to produce electric current under full load and can therefore utilize the full capacity of the pumped storage power station at an appropriate efficiency and in a timely manner. This operating method is not adapted to stabilize or improve the quality of a small local power supply system having a demand for electricity that is rather negligible as compared with the capacity of the pumped storage power station. Centrally used battery storage devices are currently under construction with the objective to put into practice a pilot operating method for grid-stabilizing (non-localized) tasks (reserve energy). However, the devices that have been planned so far do not fulfill any localized tasks. However, because of their ratio between performance, capacity and aging, battery accumulators are not very suitable for applications with several load cycles per day.
Local energy storages are generally optimized for stabilization of the local power demand and not designed or qualified for delivery of control energy to support the non-local power supply grid. Connection of the local accumulators into a facility that has a non-local as well as a local effect does not take place yet.
Therefore, it would be desirable to provide an energy storage system that at the same time permits the improvement of local power quality and supply safety for non-local power supply grid and thus can be operated as an energy storage system with sufficient effect for both purposes.